1. Field
The present disclosure relates to integrated modules. More specifically, the present disclosure relates to a hybrid integrated module that includes a semiconductor die mechanically coupled to an integrated device in which the substrate has been removed.
2. Related Art
The operating wavelengths of optical components, such as ring modulators, eschelle grating and ring-filtering devices, often differ from their target values. Origins of this difference include: process variability, manufacturing tolerances, and wafer thickness variations (notably, in the silicon device layer of silicon-on-insulator or SOI wafers). In the case of ring-resonator filters, these factors can affect the critical dimensions (CDs) of the ring resonator, with a corresponding impact on the propagating optical mode. Similar dependences have been observed in CMOS manufacturing, such as the performance dependence of an electronic device on the transistor-gate CD. In that case, continuous monitoring and optimization have been used to significantly reduce variations in the transistor-gate CD, thereby ensuring high VLSI yield and reliability. However, optical ring circuits are more susceptible to variations in CDs, even when they are fabricated using the same CMOS tool set and manufacturing standards. For example, 3σ wafer thickness variations on an SOI wafer or from wafer to wafer of 5% can shift the resonant wavelength by up to the free-spectral range (FSR) of a ring resonator.
Furthermore, silicon is characterized by a high thermo-optic coefficient, such that the resonant wavelength of a ring resonator fabricated on silicon can be tuned by changing the temperature, for example, by using thermal heaters proximate to the ring-resonator waveguide. Therefore, thermal tuning can be used to compensate for the differences between operating and target wavelengths. For example, using thermal tuning ring-resonator devices in an optical link can be matched to each other and their light sources.
However, depending on the device design, thermal tuning can consume significant power. In CMOS-based ring resonators, the heat generated in the ring resonator is dissipated through heat spreading in the silicon substrate and in the inter-layer dielectric stack up. Because the thermal conductivity of the crystalline silicon substrate underneath the ring resonator is very large, a significant fraction of system power is typically used to shift the ring resonance across its FSR to align to an appropriate optical channel and to correct mismatches corresponding to phase shifts up to 2π.
Hence, what is needed is an integrated module that can be thermally tuned without the above-described problems.